Vertical pulverizing apparatuses are used as fuel supply units in coal fired boiler plants for thermal power generation in which pulverized coal is burned as fuel.
FIG. 7 is a schematic configuration view of a background-art vertical pulverizing apparatus. As shown in FIG. 7, the vertical pulverizing apparatus is mainly constituted by a drive portion A, a pulverization portion B, a classification portion C and a distribution portion D, and the portions have a layout as illustrated.
The drive portion A has a mechanism in which torque is transmitted to a pulverizing table reduction gear 50 from a pulverizing table driving motor 51 placed outside the vertical pulverizing apparatus, and torque of the reduction gear 50 is transmitted to a pulverizing table 2 placed in an upper part of the drive portion A.
In the pulverization portion B, a plurality of pulverizing rollers 3 disposed circumferentially at equal intervals on the pulverizing table 2 are supported by a pressure frame 5, roller pivots 7 and roller brackets 6. The pressure frame 5 disposed inside the vertical pulverizing apparatus is pulled downward through a pressure rod 8 by a pressure device 9 such as a hydraulic cylinder placed outside the vertical pulverizing apparatus, so that a pulverization load can be applied to the roller brackets 6 placed under the pressure frame 5.
Due to the rotation of the pulverizing table 2, the pulverizing rollers 3 rotate together with the pulverizing table 2. Coal 60 inputted through a coal feeding pipe 1 is pulverized by a meshing part between the pulverizing table 2 and each pulverizing roller 3.
The classification portion C is placed above the pulverization portion B and provided with a rotary type classification mechanism 20 having a large number of rotary fins 21. The rotary fins 21 are disposed circumferentially at equal intervals around a hollow rotation shaft 22 disposed on the outer side of the coal feeding pipe 1, and supported by the rotation shaft 22, so that the rotary fins 21 can be rotationally driven through the rotary shaft 22 by a rotary fin driving motor 23.
On the radially outer side of the rotary fins 21, a plurality of fixed fins 12 are disposed circumferentially at equal intervals. The fixed fins 12 are hung on a ceiling part 10 of the vertical pulverizing apparatus. A cone-shaped recovery hopper 11 is coupled to the bottoms of the fixed fins 12. A bottom end opening part (not shown) of the recovery hopper 11 is opened toward the top surfaces of the center portions of the pulverizing rollers 3.
The distribution portion D is placed above the rotary type classification mechanism 20 and constituted by a distributor 33 and a plurality of distribution pipes 34 extending toward a boiler apparatus.
Incidentally, the reference numeral 4 in FIG. 7 represents a throat provided in the outer periphery of the pulverizing table 2; 30, a primary air duct; 31, a primary air wind box; and 32, a housing which receives various members.
Next, the operation of the vertical pulverizing apparatus will be described.
The coal 60 fed from the coal feeding pipe 1 falls down to the central part of the pulverizing table 2 as shown by the arrow. The pulverizing table 2 is rotationally driven through the reduction gear 50 by the driving motor 51. The coal 60 falling down onto the pulverizing table 2 is moved on the pulverizing table 2 toward the outer peripheral part thereof while drawing a spiral locus due to centrifugal force caused by the rotation. Then, the coal 60 is bitten and pulverized between the pulverizing table 2 and each pulverizing roller 3.
A group of particles 62 produced by the pulverization are blown upward above the pulverizing table 2 by conveying primary air 61 introduced from the throat 4 provided in the outer periphery of the pulverizing table 2. Of the group of particles 62 blown upward, particles with a large particle size fall down by gravity on the way of being conveyed to the classification portion C, and are returned to the pulverization portion B (primary classification).
The group of particles 62 arriving at the classification portion C are classified into fine particles 63 which are not larger than a predetermined particle size and coarse particles 64 which are larger than the predetermined particle size by the fixed fins 12 and the rotary fins 21 (secondary classification). The coarse particles 64 recovered by the recovery hopper 11 fall down to the pulverization portion B and are pulverized again. On the other hand, the fine particles 63 passing through the fixed fins 12 and the rotary fins 21 are distributed to the plurality of distribution pipes 34 in the distributor 33, and conveyed to a burner of a not-shown boiler apparatus in the form of a vapor phase.
An example of the throat 4 in the background-art vertical pulverizing apparatus is shown in FIG. 8 and FIG. 9. FIG. 8 is a sectional view showing the vicinities of the throat 4, and FIG. 9 is a development view of the throat 4.
As shown in FIG. 8, the throat 4 is an annular flow channel surrounded by a throat inner peripheral wall 41 and a throat outer peripheral wall 42. In order to enhance the primary classification, a large number of throat vanes 40 inclined at a desired angle α with respect to a rotation direction X of the pulverizing table 2 are placed at intervals in the circumferential direction of the throat 4 so as to give a turning force to the primary air 61 jetted from the throat 4.
An annular slope part 43 is placed between the housing 32 and the throat outer peripheral wall 42 so as to be lowered from the housing 32 toward the throat outer peripheral wall 42. Although the throat 4 is a rotary type throat rotating together with the pulverizing table 2 in this example, a fixed type throat attached to the housing 32 may be used as the throat 4.
When a flammable material such as coal which is pulverized by the vertical pulverizing apparatus is deposited locally inside the vertical pulverizing apparatus, there is a danger that the deposited flammable material may be heated by the high-temperature primary air 61 supplied from the throat 4, resulting in ignition.
Therefore, as shown in FIG. 8, the slope part 43 is provided so that particles 68 falling down along the inner peripheral wall surface of the housing 32 can be moved to the top of the throat 4 quickly without being deposited. It is generally thought that the slope angle of the slope part 43 has to be made not smaller than 30 degrees in view of the repose angle of powder.
It is also thought that it is desirable that the throat inner peripheral wall 41 and the throat outer peripheral wall 42 are inclined toward the central axis of the vertical pulverizing apparatus. This is to vertically blow particles supplied from the pulverizing table 2 to the top of the throat 4. That is, inward momentum is given to the primary air 61 jetted from the throat 4 in order to cancel outward momentum of the particles.
Further, when the throat vanes 40 are shaped into rectangles, manufacturing can be made easy. As shown in FIG. 8, therefore, each throat vane 40 has a top end surface 40a inclined to be higher on its outer side.